Modern telephones are completely modular in design. Installing a phone in nearly all cases is simply a matter of plugging the phone into an existing wall jack.
One of the problems inherent in such a convenient arrangement is that unauthorized persons can easily use a phone jack that is in service at the time. Having the phone company discontinue service to a given jack is both expensive and time consuming. Accordingly, there have been many devices patented to protect an active jack from unauthorized users.
"Telephone Lock" by McDaid, U.S. Pat. No. 4,964,284, discloses a device which has a plug portion which blocks the jack from unauthorized use. McDaid has the locking mechanism external to the phone jack.
"Modular Telephone Jack Lock" by Kidney, U.S. Pat. No. 4,311,883, discloses another device with a locking plug. Kidney also has an external locking mechanism and includes means for securing the phone itself.
Another McDaid device, U.S. Pat. No. 5,119,419, provides a means for securing a phone in a jack, but does not appear to disclose a means to secure an unused jack.
There are also several devices which do not actually plug the jack, but rather are attached to the wall near the jack, then physically cover the jack in a lockable manner. The "Locking Device for Telephone Subscriber Plugs" by Carney, et al., U.S. Pat. No. 4,740,168; the "Jack Security Device" of Marson, et al., U.S. Pat. No. 4,911,646; and the "Security Cover" of Petersdorff, etal., U.S. Pat. No. 4,584,856; are all examples of the covering type of device utilized to secure an active wall jack.
One shortcoming of the prior art is that all of the devices utilize hardware that is external to the jack itself. In areas where space or aesthetics is a consideration, this may not be acceptable.
Another problem that exists in the prior art is that the devices require significant effort to install, or the devices are complex enough and require sufficient hardware so that manufacturing costs are prohibitively high.